Partial uncoupling of salt gland blood flow and secretion in the Pekin duck (Anas platyrhynchos).

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RESUMO

1. The aim of this study was to investigate the relationship between the blood flow through and the secretion by the salt glands of conscious, salt-water-adapted Pekin ducks. 2. Intravenous loading with hypertonic saline induced a steady-state secretion from the salt glands with a concomitant increase in whole-organ blood flow. The distribution of elevated local glandular blood flow was, however, uneven and in addition demonstrated vasomotor patterns that ranged from constant to rhythmic. 3. During on-going salt gland secretion, the infusion of three vasoactive agents, 5Val-angiotensin II (ANG II), 8Arg-vasotocin (AVT) and noradrenaline, via the carotid artery had differential effects on salt gland blood flow and secretion. 4. ANG II (80 pmol min-1 (kg body wt)-1) had no effect on mean arterial blood pressure (MABP), produced a transient 30% decrease in glandular blood flow and strongly diminished salt gland secretion (retention of 6.4 mosmol NaCl). 5. AVT (20 pmol min-1 (kg body wt)-1) had no effect on MABP and did not alter salt gland secretion despite a 35% reduction in blood flow. 6. Noradrenaline (20 nmol min-1 (kg body wt)-1) elevated MABP by 15 mmHg, reduced salt gland blood flow by more than 50%, but diminished salt gland secretion only slightly (retention of 2.7 mosmol NaCl). 7. Using ANG II, AVT and noradrenaline as hormonal tools, integrated changes in blood flow rate did not correspond with integrated changes in salt gland excretion. The partial dissociation between both parameters shows that control of secretion by the salt gland is more complex than simply being linearly dependent upon blood flow through it.

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